1. Field of the Invention
This invention relates generally to transducer suspension systems for magnetic recording media, and more particularly to low-profile flexures that connect a transducer head with a load beam.
2. Description of the Related Art
Direct access storage devices (DASDs) such as disk drives store information on concentric tracks of a rotatable magnetic recording disk. In order to read or record the desired information on a rotating disk, a magnetic head or other transducer element on a suspension arm is moved from track to track by a rotary or linear actuator. The suspension arm is part of a head suspension assembly that typically includes a load beam attached to an actuator arm, a flexible member (known as a flexure) connected to the load beam, and a transducer head attached to the flexure. The magnetic heads, which actually read or write data on the disk, are positioned within an air-bearing slider. While the disk rotates, the slider "flies" slightly above the surface of the rotating disk, the load beam supports the slider, and the flexure allows it to gimbal to adjust its orientation for unavoidable disk surface run out or flatness variations.
Examples of suspension systems are shown in the following references: U.S. Pat. No. 5,377,064 to Yaginuma et al., issued Dec. 27, 1994; U.S. Pat. No. 5,282,102 to Christianson, issued Jan. 25, 1994; U.S. Pat. No. 5,225,950 to Crane, issued Jul. 6, 1993; U.S. Pat. No. 5,198,945 to Blaeser et al., issued Mar. 30, 1993; U.S. Pat. No. 5,187,625 to Blaeser et al., issued Feb. 16, 1993; U.S. Pat. No. 5,115,363 to Khan et al., issued May 19, 1992; U.S. Pat. No. 4,996,623 to Erpelding et al., issued Feb. 26, 1991; U.S. Pat. No. 4,797,763 to Levy et al., issued Jan. 10, 1989; U.S. Pat. No. 4,761,699 to Ainslie et al., issued Aug. 2, 1988. European Patent Application Publication No. 0487914A2 to Foote et al., published Jun. 03, 1992; PCT Publication No. WO94/24664 for Jurgenson, published Oct. 27, 1994; PCT Publication No. WO 94/16438 for Budde, published Jul. 21, 1994; PCT Publication No. WO 94/12974 for Budde, published Jun. 9, 1994 and Japanese Patent Publication No. 59-207065 for Hashimoto, published Nov. 24, 1984.
A flexure must provide a proper pivotal connection for the slider so that during operation, the slider can compensate for irregularities in manufacture and operation by pitching and/or rolling slightly in order to maintain the air bearing while maintaining appropriate stiffness against yaw movement. Pitch is defined as rotation about an axis extending directly out from the actuator arm in the plane of the disk, and roll is defined as rotation about an axis perpendicular to the pitch axis but still lying in the plane of the disk. Yaw is gyration around an axis perpendicular to the air-bearing surface. In order to be useful, any flexure must achieve low enough pitch and roll stiffness for the air bearing flying height tolerances while at the same time achieving high enough yaw stiffness.
In some suspension assemblies, the flexure is integral with the load beam; i.e., it is formed from the same sheet of metal. In other suspension assemblies, the flexure is manufactured separately and then affixed to a load beam.
Two-part load beams include a dimple to provide preload between the flexure and the main body of the load beam. For example U.S. Pat. No. 5,377,064 discloses a flexure in FIG. 12 that has a bonding pad including an upwardly facing dimple formed therein. The dimple is designed to be pushed against a portion of the load beam, thereby preloading the transducer head. Two-piece load beams with a dimple can advantageously supply substantial preload because the dimple is very stiff. However, two-piece load beams have disadvantages including increased cost of manufacturing. Particularly, the two pieces each must be separately tracked in inventory control, additional tooling is required to handle each part, and each part must be inspected. Furthermore, additional steps are necessary to manufacture a two-piece load beam and flexure, and there is an increase in the number of rejected parts. Integral flexures can solve many of these problems.
One example of an integral flexure is disclosed in U.S. Pat. No. 5,282,102 to Christianson, which shows two separate bonding pads connected by a torsion bar. The transducer head is connected to both bonding pads. The bonding pad torsion bar is connected to a load beam torsion bar that extends across an opening on the tip of the load beam. As shown, for example in FIG. 7B of U.S. Pat. No. 5,282,102, the bonding pad and torsion bar assembly stamped to allow clearance for pitching and rolling of the transducer head. Integral flexures have advantages of simplicity and a low cost of manufacture because they can be formed by an etching process at little additional cost. One disadvantage is that preloading the transducer head is usually accomplished by stamping (deforming the metal by pressure), a process that is difficult to control precisely.
One drawback of conventional integral flexures such as disclosed above is that, because the slider preload is delivered by a thin partially etched feature acting in bending alone or in combination with in-plane forces, preload forces have been limited to small values. If preload were to be increased in these conventional flexures, the flexure would be either over-stressed or deflected beyond acceptable values, causing undesirable interference between the flexure and the slider. In a conventional integral flexure, stiffness is directly related to its thickness, but stress relates to the square of thickness and deflection relates to its to the cube. In general, this means that stress and, in particular, deflection, will often dominate the behavior of the flexure.
Large capacity disk drives typically have multiple disks mounted on the same rotating spindle. The multiple disk configuration advantageously provides greater storage within the fixed size constraints imposed by industry standards such as the form factor package. Disk-to-disk spacing in a range from 2.4 mm to 4.0 mm is near the limits of current technology and imposes a limit upon the number of disks that can fit in a form factor package. In order to accommodate even more disks within the same height, it would be advantageous to reduce the disk-to-disk spacing even further.
To provide closer disk-to-disk spacing it is important that a suspension system has a very low profile. In very small disk-to-disk spacing environments, the solid height of the HGA ("Head Gimbal Assembly") must be small enough to fit within the spacing between disks. The solid height of the HGA is defined as the distance from the slider's air bearing surface to the most distant HGA feature above the slider. For example, in a conventional two-piece suspension that has a dimple to provide preload, the suspension profile includes the flexure bond pad thickness, the dimple height, the load beam thickness and the thickness of the load beam stiffeners-or flanges-if they are oriented upwardly (away from the slider). Of course, if the flanges are oriented downwardly, then they do not contribute to the suspension profile. The solid height can be reduced by choosing the thinnest possible slider and routing the signal wires on the suspension side, instead of above it. Solid height can be reduced further by improving the profile of the suspension.
It would be an advantage to provide a load beam with an integral flexure that can provide substantial preload to allow pitching and rolling movements while substantially preventing yaw movement. It would be a further advantage if the integral flexure had a very low profile to be used in close disk-to-disk spacing applications.